The functions described in this chapter will let you handle and raise Python exceptions. It is important to understand some of the basics of Python exception handling. It works somewhat like the POSIX errno
variable: there is a global indicator (per thread) of the last error that occurred. Most C API functions don?t clear this on success, but will set it to indicate the cause of the error on failure. Most C API functions also return an error indicator, usually NULL
if they are supposed to return a pointer, or -1
if they return an integer (exception: the PyArg_*()
functions return 1
for success and 0
for failure).
Concretely, the error indicator consists of three object pointers: the exception's type, the exception's value, and the traceback object. Any of those pointers can be NULL
if non-set (although some combinations are forbidden, for example you can?t have a non-NULL
traceback if the exception type is NULL
).
When a function must fail because some function it called failed, it generally doesn?t set the error indicator; the function it called already set it. It is responsible for either handling the error and clearing the exception or returning after cleaning up any resources it holds (such as object references or memory allocations); it should not continue normally if it is not prepared to handle the error. If returning due to an error, it is important to indicate to the caller that an error has been set. If the error is not handled or carefully propagated, additional calls into the Python/C API may not behave as intended and may fail in mysterious ways.
Note
The error indicator is not the result of sys.exc_info()
. The former corresponds to an exception that is not yet caught (and is therefore still propagating), while the latter returns an exception after it is caught (and has therefore stopped propagating).
PyErr_Clear
Clear the error indicator. If the error indicator is not set, there is no effect.
PyErr_PrintEx
Print a standard traceback to sys.stderr
and clear the error indicator. Unless the error is a SystemExit
, in that case no traceback is printed and the Python process will exit with the error code specified by the SystemExit
instance.
Call this function only when the error indicator is set. Otherwise it will cause a fatal error!
If set_sys_last_vars is nonzero, the variables sys.last_type
, sys.last_value
and sys.last_traceback
will be set to the type, value and traceback of the printed exception, respectively.
PyErr_Print
Alias for PyErr_PrintEx(1)
.
PyErr_WriteUnraisable
Call sys.unraisablehook()
using the current exception and obj argument.
This utility function prints a warning message to sys.stderr
when an exception has been set but it is impossible for the interpreter to actually raise the exception. It is used, for example, when an exception occurs in an __del__()
method.
The function is called with a single argument obj that identifies the context in which the unraisable exception occurred. If possible, the repr of obj will be printed in the warning message.
An exception must be set when calling this function.
These functions help you set the current thread's error indicator. For convenience, some of these functions will always return a NULL
pointer for use in a return
statement.
PyErr_SetString
This is the most common way to set the error indicator. The first argument specifies the exception type; it is normally one of the standard exceptions, e.g. PyExc_RuntimeError
. You need not increment its reference count. The second argument is an error message; it is decoded from 'utf-8
?.
PyErr_SetObject
This function is similar to PyErr_SetString()
but lets you specify an arbitrary Python object for the ?value? of the exception.
PyErr_Format
This function sets the error indicator and returns NULL
. exception should be a Python exception class. The format and subsequent parameters help format the error message; they have the same meaning and values as in PyUnicode_FromFormat()
. format is an ASCII-encoded string.
PyErr_FormatV
Same as PyErr_Format()
, but taking a va_list
argument rather than a variable number of arguments.
New in version 3.5.
PyErr_BadArgument
This is a shorthand for PyErr_SetString(PyExc_TypeError, message)
, where message indicates that a built-in operation was invoked with an illegal argument. It is mostly for internal use.
PyErr_NoMemory
This is a shorthand for PyErr_SetNone(PyExc_MemoryError)
; it returns NULL
so an object allocation function can write return PyErr_NoMemory();
when it runs out of memory.
PyErr_SetFromErrno
This is a convenience function to raise an exception when a C library function has returned an error and set the C variable errno
. It constructs a tuple object whose first item is the integer errno
value and whose second item is the corresponding error message (gotten from strerror()
), and then calls PyErr_SetObject(type, object)
. On Unix, when the errno
value is EINTR
, indicating an interrupted system call, this calls PyErr_CheckSignals()
, and if that set the error indicator, leaves it set to that. The function always returns NULL
, so a wrapper function around a system call can write return PyErr_SetFromErrno(type);
when the system call returns an error.
PyErr_SetFromErrnoWithFilenameObject
Similar to PyErr_SetFromErrno()
, with the additional behavior that if filenameObject is not NULL
, it is passed to the constructor of type as a third parameter. In the case of OSError
exception, this is used to define the filename
attribute of the exception instance.
PyErr_SetFromErrnoWithFilenameObjects
Similar to PyErr_SetFromErrnoWithFilenameObject()
, but takes a second filename object, for raising errors when a function that takes two filenames fails.
New in version 3.4.
PyErr_SetFromErrnoWithFilename
Similar to PyErr_SetFromErrnoWithFilenameObject()
, but the filename is given as a C string. filename is decoded from the filesystem encoding (os.fsdecode()
).
PyErr_SetFromWindowsErr
This is a convenience function to raise WindowsError
. If called with ierr of 0
, the error code returned by a call to GetLastError()
is used instead. It calls the Win32 function FormatMessage()
to retrieve the Windows description of error code given by ierr or GetLastError()
, then it constructs a tuple object whose first item is the ierr value and whose second item is the corresponding error message (gotten from FormatMessage()
), and then calls PyErr_SetObject(PyExc_WindowsError, object)
. This function always returns NULL
.
Availability: Windows.
PyErr_SetExcFromWindowsErr
Similar to PyErr_SetFromWindowsErr()
, with an additional parameter specifying the exception type to be raised.
Availability: Windows.
PyErr_SetFromWindowsErrWithFilename
Similar to PyErr_SetFromWindowsErrWithFilenameObject()
, but the filename is given as a C string. filename is decoded from the filesystem encoding (os.fsdecode()
).
Availability: Windows.
PyErr_SetExcFromWindowsErrWithFilenameObject
Similar to PyErr_SetFromWindowsErrWithFilenameObject()
, with an additional parameter specifying the exception type to be raised.
Availability: Windows.
PyErr_SetExcFromWindowsErrWithFilenameObjects
Similar to PyErr_SetExcFromWindowsErrWithFilenameObject()
, but accepts a second filename object.
Availability: Windows.
New in version 3.4.
PyErr_SetExcFromWindowsErrWithFilename
Similar to PyErr_SetFromWindowsErrWithFilename()
, with an additional parameter specifying the exception type to be raised.
Availability: Windows.
PyErr_SetImportError
This is a convenience function to raise ImportError
. msg will be set as the exception's message string. name and path, both of which can be NULL
, will be set as the ImportError
's respective name
and path
attributes.
New in version 3.3.
PyErr_SyntaxLocationObject
Set file, line, and offset information for the current exception. If the current exception is not a SyntaxError
, then it sets additional attributes, which make the exception printing subsystem think the exception is a SyntaxError
.
New in version 3.4.
PyErr_SyntaxLocationEx
Like PyErr_SyntaxLocationObject()
, but filename is a byte string decoded from the filesystem encoding (os.fsdecode()
).
New in version 3.2.
PyErr_SyntaxLocation
Like PyErr_SyntaxLocationEx()
, but the col_offset parameter is omitted.
PyErr_BadInternalCall
This is a shorthand for PyErr_SetString(PyExc_SystemError, message)
, where message indicates that an internal operation (e.g. a Python/C API function) was invoked with an illegal argument. It is mostly for internal use.
Use these functions to issue warnings from C code. They mirror similar functions exported by the Python warnings
module. They normally print a warning message to sys.stderr; however, it is also possible that the user has specified that warnings are to be turned into errors, and in that case they will raise an exception. It is also possible that the functions raise an exception because of a problem with the warning machinery. The return value is 0
if no exception is raised, or -1
if an exception is raised. (It is not possible to determine whether a warning message is actually printed, nor what the reason is for the exception; this is intentional.) If an exception is raised, the caller should do its normal exception handling (for example, Py_DECREF()
owned references and return an error value).
PyErr_WarnEx
Issue a warning message. The category argument is a warning category (see below) or NULL
; the message argument is a UTF-8 encoded string. stack_level is a positive number giving a number of stack frames; the warning will be issued from the currently executing line of code in that stack frame. A stack_level of 1 is the function calling PyErr_WarnEx()
, 2 is the function above that, and so forth.
Warning categories must be subclasses of PyExc_Warning
; PyExc_Warning
is a subclass of PyExc_Exception
; the default warning category is PyExc_RuntimeWarning
. The standard Python warning categories are available as global variables whose names are enumerated at Standard Warning Categories.
For information about warning control, see the documentation for the warnings
module and the -W
option in the command line documentation. There is no C API for warning control.
PyErr_SetImportErrorSubclass
Much like PyErr_SetImportError()
but this function allows for specifying a subclass of ImportError
to raise.
New in version 3.6.
PyErr_WarnExplicitObject
Issue a warning message with explicit control over all warning attributes. This is a straightforward wrapper around the Python function warnings.warn_explicit()
, see there for more information. The module and registry arguments may be set to NULL
to get the default effect described there.
New in version 3.4.
PyErr_WarnExplicit
Similar to PyErr_WarnExplicitObject()
except that message and module are UTF-8 encoded strings, and filename is decoded from the filesystem encoding (os.fsdecode()
).
PyErr_WarnFormat
Function similar to PyErr_WarnEx()
, but use PyUnicode_FromFormat()
to format the warning message. format is an ASCII-encoded string.
New in version 3.2.
PyErr_ResourceWarning
Function similar to PyErr_WarnFormat()
, but category is ResourceWarning
and pass source to warnings.WarningMessage()
.
New in version 3.6.
PyErr_Occurred
Test whether the error indicator is set. If set, return the exception type (the first argument to the last call to one of the PyErr_Set*()
functions or to PyErr_Restore()
). If not set, return NULL
. You do not own a reference to the return value, so you do not need to Py_DECREF()
it.
Note
Do not compare the return value to a specific exception; use PyErr_ExceptionMatches()
instead, shown below. (The comparison could easily fail since the exception may be an instance instead of a class, in the case of a class exception, or it may be a subclass of the expected exception.)
PyErr_ExceptionMatches
Equivalent to PyErr_GivenExceptionMatches(PyErr_Occurred(), exc)
. This should only be called when an exception is actually set; a memory access violation will occur if no exception has been raised.
PyErr_GivenExceptionMatches
Return true if the given exception matches the exception type in exc. If exc is a class object, this also returns true when given is an instance of a subclass. If exc is a tuple, all exception types in the tuple (and recursively in subtuples) are searched for a match.
PyErr_Fetch
Retrieve the error indicator into three variables whose addresses are passed. If the error indicator is not set, set all three variables to NULL
. If it is set, it will be cleared and you own a reference to each object retrieved. The value and traceback object may be NULL
even when the type object is not.
Note
This function is normally only used by code that needs to catch exceptions or by code that needs to save and restore the error indicator temporarily, e.g.:
{
PyObject *type, *value, *traceback;
PyErr_Fetch(&type, &value, &traceback);
/* ... code that might produce other errors ... */
PyErr_Restore(type, value, traceback);
}
PyErr_Restore
Set the error indicator from the three objects. If the error indicator is already set, it is cleared first. If the objects are NULL
, the error indicator is cleared. Do not pass a NULL
type and non-NULL
value or traceback. The exception type should be a class. Do not pass an invalid exception type or value. (Violating these rules will cause subtle problems later.) This call takes away a reference to each object: you must own a reference to each object before the call and after the call you no longer own these references. (If you don?t understand this, don?t use this function. I warned you.)
Note
This function is normally only used by code that needs to save and restore the error indicator temporarily. Use PyErr_Fetch()
to save the current error indicator.
PyErr_NormalizeException
Under certain circumstances, the values returned by PyErr_Fetch()
below can be ?unnormalized?, meaning that *exc
is a class object but *val
is not an instance of the same class. This function can be used to instantiate the class in that case. If the values are already normalized, nothing happens. The delayed normalization is implemented to improve performance.
Note
This function does not implicitly set the __traceback__
attribute on the exception value. If setting the traceback appropriately is desired, the following additional snippet is needed:
if (tb != NULL) {
PyException_SetTraceback(val, tb);
}
PyErr_GetExcInfo
Retrieve the exception info, as known from sys.exc_info()
. This refers to an exception that was already caught, not to an exception that was freshly raised. Returns new references for the three objects, any of which may be NULL
. Does not modify the exception info state.
Note
This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use PyErr_SetExcInfo()
to restore or clear the exception state.
New in version 3.3.
PyErr_SetExcInfo
Set the exception info, as known from sys.exc_info()
. This refers to an exception that was already caught, not to an exception that was freshly raised. This function steals the references of the arguments. To clear the exception state, pass NULL
for all three arguments. For general rules about the three arguments, see PyErr_Restore()
.
Note
This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use PyErr_GetExcInfo()
to read the exception state.
New in version 3.3.
PyErr_CheckSignals
This function interacts with Python's signal handling. It checks whether a signal has been sent to the processes and if so, invokes the corresponding signal handler. If the signal
module is supported, this can invoke a signal handler written in Python. In all cases, the default effect for SIGINT
is to raise the KeyboardInterrupt
exception. If an exception is raised the error indicator is set and the function returns -1
; otherwise the function returns 0
. The error indicator may or may not be cleared if it was previously set.
PyErr_SetInterrupt
Simulate the effect of a SIGINT
signal arriving. The next time PyErr_CheckSignals()
is called, the Python signal handler for SIGINT
will be called.
If SIGINT
isn?t handled by Python (it was set to signal.SIG_DFL
or signal.SIG_IGN
), this function does nothing.
PySignal_SetWakeupFd
This utility function specifies a file descriptor to which the signal number is written as a single byte whenever a signal is received. fd must be non-blocking. It returns the previous such file descriptor.
The value -1
disables the feature; this is the initial state. This is equivalent to signal.set_wakeup_fd()
in Python, but without any error checking. fd should be a valid file descriptor. The function should only be called from the main thread.
Changed in version 3.5: On Windows, the function now also supports socket handles.
PyErr_NewException
This utility function creates and returns a new exception class. The name argument must be the name of the new exception, a C string of the form module.classname
. The base and dict arguments are normally NULL
. This creates a class object derived from Exception
(accessible in C as PyExc_Exception
).
The __module__
attribute of the new class is set to the first part (up to the last dot) of the name argument, and the class name is set to the last part (after the last dot). The base argument can be used to specify alternate base classes; it can either be only one class or a tuple of classes. The dict argument can be used to specify a dictionary of class variables and methods.
PyErr_NewExceptionWithDoc
Same as PyErr_NewException()
, except that the new exception class can easily be given a docstring: If doc is non-NULL
, it will be used as the docstring for the exception class.
New in version 3.2.
PyException_GetTraceback
Return the traceback associated with the exception as a new reference, as accessible from Python through __traceback__
. If there is no traceback associated, this returns NULL
.
PyException_SetTraceback
Set the traceback associated with the exception to tb. Use Py_None
to clear it.
PyException_GetContext
Return the context (another exception instance during whose handling ex was raised) associated with the exception as a new reference, as accessible from Python through __context__
. If there is no context associated, this returns NULL
.
PyException_SetContext
Set the context associated with the exception to ctx. Use NULL
to clear it. There is no type check to make sure that ctx is an exception instance. This steals a reference to ctx.
PyException_GetCause
Return the cause (either an exception instance, or None
, set by raise ... from ...
) associated with the exception as a new reference, as accessible from Python through __cause__
.
PyException_SetCause
Set the cause associated with the exception to cause. Use NULL
to clear it. There is no type check to make sure that cause is either an exception instance or None
. This steals a reference to cause.
__suppress_context__
is implicitly set to True
by this function.
The following functions are used to create and modify Unicode exceptions from C.
PyUnicodeDecodeError_Create
Create a UnicodeDecodeError
object with the attributes encoding, object, length, start, end and reason. encoding and reason are UTF-8 encoded strings.
PyUnicodeEncodeError_Create
Create a UnicodeEncodeError
object with the attributes encoding, object, length, start, end and reason. encoding and reason are UTF-8 encoded strings.
PyUnicodeTranslateError_Create
Create a UnicodeTranslateError
object with the attributes object, length, start, end and reason. reason is a UTF-8 encoded string.
PyUnicodeDecodeError_GetEncoding
PyUnicodeEncodeError_GetEncoding
Return the encoding attribute of the given exception object.
PyUnicodeDecodeError_GetObject
PyUnicodeEncodeError_GetObject
PyUnicodeTranslateError_GetObject
Return the object attribute of the given exception object.
PyUnicodeDecodeError_GetStart
PyUnicodeEncodeError_GetStart
PyUnicodeTranslateError_GetStart
Get the start attribute of the given exception object and place it into *start. start must not be NULL
. Return 0
on success, -1
on failure.
PyUnicodeDecodeError_SetStart
PyUnicodeEncodeError_SetStart
PyUnicodeTranslateError_SetStart
Set the start attribute of the given exception object to start. Return 0
on success, -1
on failure.
PyUnicodeDecodeError_GetEnd
PyUnicodeEncodeError_GetEnd
PyUnicodeTranslateError_GetEnd
Get the end attribute of the given exception object and place it into *end. end must not be NULL
. Return 0
on success, -1
on failure.
PyUnicodeDecodeError_SetEnd
PyUnicodeEncodeError_SetEnd
PyUnicodeTranslateError_SetEnd
Set the end attribute of the given exception object to end. Return 0
on success, -1
on failure.
PyUnicodeDecodeError_GetReason
PyUnicodeEncodeError_GetReason
PyUnicodeTranslateError_GetReason
Return the reason attribute of the given exception object.
PyUnicodeDecodeError_SetReason
PyUnicodeEncodeError_SetReason
PyUnicodeTranslateError_SetReason
Set the reason attribute of the given exception object to reason. Return 0
on success, -1
on failure.
These two functions provide a way to perform safe recursive calls at the C level, both in the core and in extension modules. They are needed if the recursive code does not necessarily invoke Python code (which tracks its recursion depth automatically).
Py_EnterRecursiveCall
Marks a point where a recursive C-level call is about to be performed.
If USE_STACKCHECK
is defined, this function checks if the OS stack overflowed using PyOS_CheckStack()
. In this is the case, it sets a MemoryError
and returns a nonzero value.
The function then checks if the recursion limit is reached. If this is the case, a RecursionError
is set and a nonzero value is returned. Otherwise, zero is returned.
where should be a string such as " in instance check"
to be concatenated to the RecursionError
message caused by the recursion depth limit.
Py_LeaveRecursiveCall
Ends a Py_EnterRecursiveCall()
. Must be called once for each successful invocation of Py_EnterRecursiveCall()
.
Properly implementing tp_repr
for container types requires special recursion handling. In addition to protecting the stack, tp_repr
also needs to track objects to prevent cycles. The following two functions facilitate this functionality. Effectively, these are the C equivalent to reprlib.recursive_repr()
.
Py_ReprEnter
Called at the beginning of the tp_repr
implementation to detect cycles.
If the object has already been processed, the function returns a positive integer. In that case the tp_repr
implementation should return a string object indicating a cycle. As examples, dict
objects return {...}
and list
objects return [...]
.
The function will return a negative integer if the recursion limit is reached. In that case the tp_repr
implementation should typically return NULL
.
Otherwise, the function returns zero and the tp_repr
implementation can continue normally.
Py_ReprLeave
Ends a Py_ReprEnter()
. Must be called once for each invocation of Py_ReprEnter()
that returns zero.
All standard Python exceptions are available as global variables whose names are PyExc_
followed by the Python exception name. These have the type PyObject*
; they are all class objects. For completeness, here are all the variables:
C Name | Python Name | Notes |
---|---|---|
| (1) | |
| (1) | |
| (1) | |
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| (1) | |
| ||
| ||
| ||
| ||
| ||
| (1) | |
| ||
| ||
| ||
| ||
| (2) | |
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
|
New in version 3.3: PyExc_BlockingIOError
, PyExc_BrokenPipeError
, PyExc_ChildProcessError
, PyExc_ConnectionError
, PyExc_ConnectionAbortedError
, PyExc_ConnectionRefusedError
, PyExc_ConnectionResetError
, PyExc_FileExistsError
, PyExc_FileNotFoundError
, PyExc_InterruptedError
, PyExc_IsADirectoryError
, PyExc_NotADirectoryError
, PyExc_PermissionError
, PyExc_ProcessLookupError
and PyExc_TimeoutError
were introduced following PEP 3151.
New in version 3.5: PyExc_StopAsyncIteration
and PyExc_RecursionError
.
New in version 3.6: PyExc_ModuleNotFoundError
.
These are compatibility aliases to PyExc_OSError
:
C Name | Notes |
---|---|
| |
| |
| (3) |
Changed in version 3.3: These aliases used to be separate exception types.
Notes:
This is a base class for other standard exceptions.
Only defined on Windows; protect code that uses this by testing that the preprocessor macro MS_WINDOWS
is defined.
All standard Python warning categories are available as global variables whose names are PyExc_
followed by the Python exception name. These have the type PyObject*
; they are all class objects. For completeness, here are all the variables:
C Name | Python Name | Notes |
---|---|---|
| (1) | |
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
| ||
|
New in version 3.2: PyExc_ResourceWarning
.
Notes:
This is a base class for other standard warning categories.
{
PyObject *type, *value, *traceback;
PyErr_Fetch(&type, &value, &traceback);
/* ... code that might produce other errors ... */
PyErr_Restore(type, value, traceback);
}
PyErr_Restore
Set the error indicator from the three objects. If the error indicator is already set, it is cleared first. If the objects are NULL
, the error indicator is cleared. Do not pass a NULL
type and non-NULL
value or traceback. The exception type should be a class. Do not pass an invalid exception type or value. (Violating these rules will cause subtle problems later.) This call takes away a reference to each object: you must own a reference to each object before the call and after the call you no longer own these references. (If you don?t understand this, don?t use this function. I warned you.)
Note
This function is normally only used by code that needs to save and restore the error indicator temporarily. Use PyErr_Fetch()
to save the current error indicator.
PyErr_NormalizeException
Under certain circumstances, the values returned by PyErr_Fetch()
below can be ?unnormalized?, meaning that *exc
is a class object but *val
is not an instance of the same class. This function can be used to instantiate the class in that case. If the values are already normalized, nothing happens. The delayed normalization is implemented to improve performance.
Note
This function does not implicitly set the __traceback__
attribute on the exception value. If setting the traceback appropriately is desired, the following additional snippet is needed:
if (tb != NULL) {
PyException_SetTraceback(val, tb);
}
PyErr_GetExcInfo
Retrieve the exception info, as known from sys.exc_info()
. This refers to an exception that was already caught, not to an exception that was freshly raised. Returns new references for the three objects, any of which may be NULL
. Does not modify the exception info state.
Note
This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use PyErr_SetExcInfo()
to restore or clear the exception state.
New in version 3.3.
PyErr_SetExcInfo
Set the exception info, as known from sys.exc_info()
. This refers to an exception that was already caught, not to an exception that was freshly raised. This function steals the references of the arguments. To clear the exception state, pass NULL
for all three arguments. For general rules about the three arguments, see PyErr_Restore()
.
Note
This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use PyErr_GetExcInfo()
to read the exception state.
New in version 3.3.
PyErr_CheckSignals
This function interacts with Python's signal handling. It checks whether a signal has been sent to the processes and if so, invokes the corresponding signal handler. If the signal
module is supported, this can invoke a signal handler written in Python. In all cases, the default effect for SIGINT
is to raise the KeyboardInterrupt
exception. If an exception is raised the error indicator is set and the function returns -1
; otherwise the function returns 0
. The error indicator may or may not be cleared if it was previously set.
PyErr_SetInterrupt
Simulate the effect of a SIGINT
signal arriving. The next time PyErr_CheckSignals()
is called, the Python signal handler for SIGINT
will be called.
If SIGINT
isn?t handled by Python (it was set to signal.SIG_DFL
or signal.SIG_IGN
), this function does nothing.
PySignal_SetWakeupFd
This utility function specifies a file descriptor to which the signal number is written as a single byte whenever a signal is received. fd must be non-blocking. It returns the previous such file descriptor.
The value -1
disables the feature; this is the initial state. This is equivalent to signal.set_wakeup_fd()
in Python, but without any error checking. fd should be a valid file descriptor. The function should only be called from the main thread.
Changed in version 3.5: On Windows, the function now also supports socket handles.
PyErr_NewException
This utility function creates and returns a new exception class. The name argument must be the name of the new exception, a C string of the form module.classname
. The base and dict arguments are normally NULL
. This creates a class object derived from Exception
(accessible in C as PyExc_Exception
).
The __module__
attribute of the new class is set to the first part (up to the last dot) of the name argument, and the class name is set to the last part (after the last dot). The base argument can be used to specify alternate base classes; it can either be only one class or a tuple of classes. The dict argument can be used to specify a dictionary of class variables and methods.
PyErr_NewExceptionWithDoc
Same as PyErr_NewException()
, except that the new exception class can easily be given a docstring: If doc is non-NULL
, it will be used as the docstring for the exception class.
New in version 3.2.
PyException_GetTraceback
Return the traceback associated with the exception as a new reference, as accessible from Python through __traceback__
. If there is no traceback associated, this returns NULL
.
PyException_SetTraceback
Set the traceback associated with the exception to tb. Use Py_None
to clear it.
PyException_GetContext
Return the context (another exception instance during whose handling ex was raised) associated with the exception as a new reference, as accessible from Python through __context__
. If there is no context associated, this returns NULL
.
PyException_SetContext
Set the context associated with the exception to ctx. Use NULL
to clear it. There is no type check to make sure that ctx is an exception instance. This steals a reference to ctx.
PyException_GetCause
Return the cause (either an exception instance, or None
, set by raise ... from ...
) associated with the exception as a new reference, as accessible from Python through __cause__
.
PyException_SetCause
Set the cause associated with the exception to cause. Use NULL
to clear it. There is no type check to make sure that cause is either an exception instance or None
. This steals a reference to cause.
__suppress_context__
is implicitly set to True
by this function.
The following functions are used to create and modify Unicode exceptions from C.
PyUnicodeDecodeError_Create
Create a UnicodeDecodeError
object with the attributes encoding, object, length, start, end and reason. encoding and reason are UTF-8 encoded strings.
PyUnicodeEncodeError_Create
Create a UnicodeEncodeError
object with the attributes encoding, object, length, start, end and reason. encoding and reason are UTF-8 encoded strings.
PyUnicodeTranslateError_Create
Create a UnicodeTranslateError
object with the attributes object, length, start, end and reason. reason is a UTF-8 encoded string.
PyUnicodeDecodeError_GetEncoding
PyUnicodeEncodeError_GetEncoding
Return the encoding attribute of the given exception object.
PyUnicodeDecodeError_GetObject
PyUnicodeEncodeError_GetObject
PyUnicodeTranslateError_GetObject
Return the object attribute of the given exception object.
PyUnicodeDecodeError_GetStart
PyUnicodeEncodeError_GetStart
PyUnicodeTranslateError_GetStart
Get the start attribute of the given exception object and place it into *start. start must not be NULL
. Return 0
on success, -1
on failure.
PyUnicodeDecodeError_SetStart
PyUnicodeEncodeError_SetStart
PyUnicodeTranslateError_SetStart
Set the start attribute of the given exception object to start. Return 0
on success, -1
on failure.
PyUnicodeDecodeError_GetEnd
PyUnicodeEncodeError_GetEnd
PyUnicodeTranslateError_GetEnd
Get the end attribute of the given exception object and place it into *end. end must not be NULL
. Return 0
on success, -1
on failure.
PyUnicodeDecodeError_SetEnd
PyUnicodeEncodeError_SetEnd
PyUnicodeTranslateError_SetEnd
Set the end attribute of the given exception object to end. Return 0
on success, -1
on failure.
PyUnicodeDecodeError_GetReason
PyUnicodeEncodeError_GetReason
PyUnicodeTranslateError_GetReason
Return the reason attribute of the given exception object.
PyUnicodeDecodeError_SetReason
PyUnicodeEncodeError_SetReason
PyUnicodeTranslateError_SetReason
Set the reason attribute of the given exception object to reason. Return 0
on success, -1
on failure.
These two functions provide a way to perform safe recursive calls at the C level, both in the core and in extension modules. They are needed if the recursive code does not necessarily invoke Python code (which tracks its recursion depth automatically).
Py_EnterRecursiveCall
Marks a point where a recursive C-level call is about to be performed.
If USE_STACKCHECK
is defined, this function checks if the OS stack overflowed using PyOS_CheckStack()
. In this is the case, it sets a MemoryError
and returns a nonzero value.
The function then checks if the recursion limit is reached. If this is the case, a RecursionError
is set and a nonzero value is returned. Otherwise, zero is returned.
where should be a string such as " in instance check"
to be concatenated to the RecursionError
message caused by the recursion depth limit.
Py_LeaveRecursiveCall
Ends a Py_EnterRecursiveCall()
. Must be called once for each successful invocation of Py_EnterRecursiveCall()
.
Properly implementing tp_repr
for container types requires special recursion handling. In addition to protecting the stack, tp_repr
also needs to track objects to prevent cycles. The following two functions facilitate this functionality. Effectively, these are the C equivalent to reprlib.recursive_repr()
.
Py_ReprEnter
Called at the beginning of the tp_repr
implementation to detect cycles.
If the object has already been processed, the function returns a positive integer. In that case the tp_repr
implementation should return a string object indicating a cycle. As examples, dict
objects return {...}
and list
objects return [...]
.
The function will return a negative integer if the recursion limit is reached. In that case the tp_repr
implementation should typically return NULL
.
Otherwise, the function returns zero and the tp_repr
implementation can continue normally.
Py_ReprLeave
Ends a Py_ReprEnter()
. Must be called once for each invocation of Py_ReprEnter()
that returns zero.
All standard Python exceptions are available as global variables whose names are PyExc_
followed by the Python exception name. These have the type PyObject*
; they are all class objects. For completeness, here are all the variables:
C Name | Python Name | Notes |
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| (1) | |
| (1) | |
| (1) | |
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| (1) | |
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| (1) | |
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| (2) | |
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New in version 3.3: PyExc_BlockingIOError
, PyExc_BrokenPipeError
, PyExc_ChildProcessError
, PyExc_ConnectionError
, PyExc_ConnectionAbortedError
, PyExc_ConnectionRefusedError
, PyExc_ConnectionResetError
, PyExc_FileExistsError
, PyExc_FileNotFoundError
, PyExc_InterruptedError
, PyExc_IsADirectoryError
, PyExc_NotADirectoryError
, PyExc_PermissionError
, PyExc_ProcessLookupError
and PyExc_TimeoutError
were introduced following PEP 3151.
New in version 3.5: PyExc_StopAsyncIteration
and PyExc_RecursionError
.
New in version 3.6: PyExc_ModuleNotFoundError
.
These are compatibility aliases to PyExc_OSError
:
C Name | Notes |
---|---|
| |
| |
| (3) |
Changed in version 3.3: These aliases used to be separate exception types.
Notes:
This is a base class for other standard exceptions.
Only defined on Windows; protect code that uses this by testing that the preprocessor macro MS_WINDOWS
is defined.
All standard Python warning categories are available as global variables whose names are PyExc_
followed by the Python exception name. These have the type PyObject*
; they are all class objects. For completeness, here are all the variables:
C Name | Python Name | Notes |
---|---|---|
| (1) | |
| ||
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|
New in version 3.2: PyExc_ResourceWarning
.
Notes:
This is a base class for other standard warning categories.